Meat extracts with acid-soluble glycogen (macroglycogen) from M. longissmus dorsi of carriers and noncarriers of the PRKAG3 mutation (RN(-) and rn(+) genotype) were analyzed by both (1)H liquid-state NMR spectroscopy and a biochemical method. The (1)H NMR analysis revealed that shorter polymers (dimers, trimers, etc.) of α-1,4-linked glucose were generated 24-48 h post-mortem. This is not possible to elucidate with the biochemical method, by which only the total amount of hydrolyzed glucose residues is determined. The shorter polymers were primarily formed in carriers of the PRKAG3 mutation, suggesting different post-mortem glycogen degradation mechanisms in the two genotypes.